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© 2007 McGraw-Hill Higher Education. All rights reserved. Chapter 10 Respiration During Exercise EXERCISE PHYSIOLOGY Theory and Application to Fitness.

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1 © 2007 McGraw-Hill Higher Education. All rights reserved. Chapter 10 Respiration During Exercise EXERCISE PHYSIOLOGY Theory and Application to Fitness and Performance, 5 th edition Scott K. Powers & Edward T. Howley

2 © 2007 McGraw-Hill Higher Education. All rights reserved. Introduction The Respiratory System –Provides a means of gas exchange between the environment and the body –Plays a role in the regulation of acid- base balance during exercise

3 © 2007 McGraw-Hill Higher Education. All rights reserved. Objectives Explain the principle physiological function of the pulmonary system Outline the major anatomical components of the respiratory system List major muscles involved in inspiration and expiration, at rest and during exercise Discuss the importance of matching blood flow to alveolar ventilation in the lung Explain how gases are transported across the blood-gas interface in the lung

4 © 2007 McGraw-Hill Higher Education. All rights reserved. Objectives Discuss the major transportation modes of O 2 and CO 2 in the blood Discuss the effects of  temp,  pH, and  levels of 2-3 DPG on the oxygen-hemoglobin dissociation curve Describe the ventilatory response to constant load, steady-state exercise

5 © 2007 McGraw-Hill Higher Education. All rights reserved. Objectives Describe the ventilatory response to incremental exercise Identify the location and function of chemoreceptors and mechanoreceptors that are thought to play a role in the regulation of breathing Discuss the neural-humoral theory of respiratory control during exercise

6 © 2007 McGraw-Hill Higher Education. All rights reserved. Respiration 1.Pulmonary respiration –Ventilation (breathing) and the exchange of gases (O 2 and CO 2 ) in the lungs 2.Cellular respiration –Relates to O 2 utilization and CO 2 production by the tissues This chapter is concerned with pulmonary respiration, and “respiration” will be used to mean such

7 © 2007 McGraw-Hill Higher Education. All rights reserved. Function of the Lungs Primary purpose is to provide a means of gas exchange between the external environment and the body Ventilation refers to the mechanical process of moving air into and out of lungs Diffusion is the random movement of molecules from an area of high concentration to an area of lower concentration

8 © 2007 McGraw-Hill Higher Education. All rights reserved. Major Organs of the Respiratory System Fig 10.1

9 © 2007 McGraw-Hill Higher Education. All rights reserved. Position of the Lungs, Diaphragm, and Pleura Fig 10.2

10 © 2007 McGraw-Hill Higher Education. All rights reserved. Conducting and Respiratory Zones Conducting zone Conducts air to respiratory zone Humidifies, warms, and filters air Components: –Trachea –Bronchial tree –Bronchioles Respiratory zone Exchange of gases between air and blood Components: –Respiratory bronchioles –Alveolar sacs

11 © 2007 McGraw-Hill Higher Education. All rights reserved. Conducting & Respiratory Zones Fig 10.2

12 © 2007 McGraw-Hill Higher Education. All rights reserved. Pathway of Air to Alveoli Fig 10.4

13 © 2007 McGraw-Hill Higher Education. All rights reserved. Mechanics of Breathing Inspiration –Diaphragm pushes downward, lowering intrapulmonary pressure Expiration –Diaphragm relaxes, raising intrapulmonary pressure Resistance to airflow –Largely determined by airway diameter

14 © 2007 McGraw-Hill Higher Education. All rights reserved. The Mechanics of Inspiration and Expiration Fig 10.6

15 © 2007 McGraw-Hill Higher Education. All rights reserved. Muscles of Respiration Fig 10.7

16 © 2007 McGraw-Hill Higher Education. All rights reserved. Pulmonary Ventilation (V) The amount of air moved in or out of the lungs per minute –Product of tidal volume (V T ) and breathing frequency (f) V = V T x f

17 © 2007 McGraw-Hill Higher Education. All rights reserved. Pulmonary Ventilation (V) Dead-space ventilation (V D ) –“Unused” ventilation –Does not participate in gas exchange –Anatomical dead space: conducting zone –Physiological dead space: disease Alveolar ventilation (V A ) –Volume of inspired gas that reaches the respiratory zone V = V A + V D

18 © 2007 McGraw-Hill Higher Education. All rights reserved. Pulmonary Volumes and Capacities Measured by spirometry Vital capacity (VC) –Maximum amount of air that can be expired following a maximum inspiration Residual volume (RV) –Air remaining in the lungs after a maximum expiration Total lung capacity (TLC) –Sum of VC and RV

19 © 2007 McGraw-Hill Higher Education. All rights reserved. Pulmonary Volumes and Capacities Fig 10.9

20 © 2007 McGraw-Hill Higher Education. All rights reserved. Partial Pressure of Gases Dalton’s Law The total pressure of a gas mixture is equal to the sum of the pressure that each gas would exert independently The partial pressure of oxygen (PO 2 ) –Air is 20.93% oxygen Expressed as a fraction: –Total pressure of air = 760 mmHg PO2 = x 760 = 159 mmHg

21 © 2007 McGraw-Hill Higher Education. All rights reserved. Diffusion of Gases Fick’s law of diffusion The rate of gas transfer (V gas) is proportional to the tissue area, the diffusion coefficient of the gas, and the difference in the partial pressure of the gas on the two sides of the tissue, and inversely proportional to the thickness. V gas = rate of diffusion D = diffusion coefficient of gas A = tissue areaP 1 -P 2 = difference in partial pressure T = tissue thickness V gas = A T x D x (P 1 -P 2 )

22 © 2007 McGraw-Hill Higher Education. All rights reserved. Partial Pressure and Gas Exchange Fig 10.10

23 © 2007 McGraw-Hill Higher Education. All rights reserved. Blood Flow to the Lung Pulmonary circuit –Same rate of flow as systemic circuit –Lower pressure Fig 10.11

24 © 2007 McGraw-Hill Higher Education. All rights reserved. Blood Flow to the Lung When standing, most of the blood flow is to the base of the lung –Due to gravitational force Fig 10.12

25 © 2007 McGraw-Hill Higher Education. All rights reserved. Ventilation-Perfusion Relationships Ventilation/perfusion ratio –Indicates matching of blood flow to ventilation –Ideal: ~1.0 Base –Overperfused (ratio <1.0) Apex –Underperfused (ratio >1.0)

26 © 2007 McGraw-Hill Higher Education. All rights reserved. Ventilation/Perfusion Ratios Fig 10.13

27 © 2007 McGraw-Hill Higher Education. All rights reserved. O 2 Transport in the Blood Approximately 99% of O 2 is transported in the blood bound to hemoglobin (Hb) –Oxyhemoglobin: O 2 bound to Hb –Deoxyhemoglobin: O 2 not bound to Hb Amount of O 2 that can be transported per unit volume of blood in dependent on the concentration of hemoglobin

28 © 2007 McGraw-Hill Higher Education. All rights reserved. Oxyhemoglobin Dissociation Curve Fig 10.14

29 © 2007 McGraw-Hill Higher Education. All rights reserved. O 2 -Hb Dissociation Curve: Effect of pH Blood pH declines during heavy exercise Results in a “rightward” shift of the curve –Bohr effect –Favors “offloading” of O 2 to the tissues Fig 10.15

30 © 2007 McGraw-Hill Higher Education. All rights reserved. O 2 -Hb Dissociation Curve: Effect of Temperature Increased blood temperature results in a weaker Hb-O 2 bond Rightward shift of curve –Easier “offloading” of O 2 at tissues Fig 10.16

31 © 2007 McGraw-Hill Higher Education. All rights reserved. O 2 -Hb Dissociation Curve: 2-3 DPG RBC must rely on anaerobic glycolysis to meet the cell’s energy demands A by-product is 2-3 DPG, which can combine with hemoglobin and reduce hemoglobin’s affinity of O DPG increase during exposure to altitude At sea level, right shift of curve not to changes in 2-3 DPG, but to degree of acidosis and blood temperature

32 © 2007 McGraw-Hill Higher Education. All rights reserved. O 2 Transport in Muscle Myoglobin (Mb) shuttles O 2 from the cell membrane to the mitochondria Higher affinity for O 2 than hemoglobin –Even at low PO 2 –Allows Mb to store O 2

33 © 2007 McGraw-Hill Higher Education. All rights reserved. Dissociation Curves for Myoglobin and Hemoglobin Fig 10.17

34 © 2007 McGraw-Hill Higher Education. All rights reserved. CO 2 Transport in Blood Dissolved in plasma (10%) Bound to Hb (20%) Bicarbonate (70%) –CO 2 + H 2 O  H 2 CO 3  H + + HCO 3 - –Also important for buffering H +

35 © 2007 McGraw-Hill Higher Education. All rights reserved. CO 2 Transport in Blood Fig 10.18

36 © 2007 McGraw-Hill Higher Education. All rights reserved. Release of CO 2 From Blood Fig 10.19

37 © 2007 McGraw-Hill Higher Education. All rights reserved. Rest-to-Work Transitions Initially, ventilation increases rapidly –Then, a slower rise toward steady-state PO 2 and PCO 2 are maintained Fig 10.20

38 © 2007 McGraw-Hill Higher Education. All rights reserved. Exercise in a Hot Environment During prolonged submaximal exercise: –Ventilation tends to drift upward –Little change in PCO 2 –Higher ventilation not due to increased PCO 2 Fig 10.21

39 © 2007 McGraw-Hill Higher Education. All rights reserved. Incremental Exercise Linear increase in ventilation –Up to ~50-75% VO 2max Exponential increase beyond this point Ventilatory threshold (T vent ) –Inflection point where V E increases exponentially

40 © 2007 McGraw-Hill Higher Education. All rights reserved. Ventilatory Response to Exercise: Trained vs. Untrained In the trained runner, –decrease in arterial PO 2 near exhaustion –pH maintained at a higher work rate –T vent occurs at a higher work rate Fig 10.22

41 © 2007 McGraw-Hill Higher Education. All rights reserved. Ventilatory Response to Exercise: Trained vs. Untrained Fig 10.22

42 © 2007 McGraw-Hill Higher Education. All rights reserved. Exercise-Induced Hypoxemia 1980s: 40-50% of elite male endurance athletes were capable of developing 1990s: 25-51% of elite female endurance athletes were also capable of developing Causes: –Ventilation-perfusion mismatch –Diffusion limitations due to reduce time of RBC in pulmonary capillaries due to high cardiac outputs

43 © 2007 McGraw-Hill Higher Education. All rights reserved. Control of Ventilation Respiratory control center –Receives neural and humoral input Feedback from muscles CO 2 level in the blood –Regulates respiratory rate Fig 10.23

44 © 2007 McGraw-Hill Higher Education. All rights reserved. Input to the Respiratory Control Centers Humoral chemoreceptors –Central chemoreceptors Located in the medulla PCO 2 and H + concentration in cerebrospinal fluid –Peripheral chemoreceptors Aortic and carotid bodies PO 2, PCO 2, H +, and K + in blood Neural input –From motor cortex or skeletal muscle

45 © 2007 McGraw-Hill Higher Education. All rights reserved. Effect of Arterial PCO 2 on Ventilation Fig 10.24

46 © 2007 McGraw-Hill Higher Education. All rights reserved. Effect of Arterial PO 2 on Ventilation Fig 10.25

47 © 2007 McGraw-Hill Higher Education. All rights reserved. Ventilatory Control During Exercise Submaximal exercise –Linear increase due to: Central command Humoral chemoreceptors Neural feedback Heavy exercise –Exponential rise above T vent Increasing blood H +

48 © 2007 McGraw-Hill Higher Education. All rights reserved. Ventilatory Control During Submaximal Exercise Fig 10.26

49 © 2007 McGraw-Hill Higher Education. All rights reserved. Effect of Training on Ventilation Ventilation is lower at same work rate following training –May be due to lower blood lactic acid levels –Results in less feedback to stimulate breathing

50 © 2007 McGraw-Hill Higher Education. All rights reserved. Effects of Endurance Training on Ventilation During Exercise Fig 10.27

51 © 2007 McGraw-Hill Higher Education. All rights reserved. Do the Lungs Limit Exercise Performance? Low-to-moderate intensity exercise –Pulmonary system not seen as a limitation Maximal exercise –Not thought to be a limitation in healthy individuals at sea level –May be limiting in elite endurance athletes –New evidence that respiratory muscle fatigue does occur during high intensity exercise

52 © 2007 McGraw-Hill Higher Education. All rights reserved. Chapter 10 Respiration During Exercise


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